The present invention relates to on-the-fly control of jitter during optical disc mastering/recording and, more particularly, to a system for the on-the-fly control of jitter that provides improved control of the start and stop positions of each recorded pit.
Optical discs, including the various types of discs known generically as compact discs and the more recent digital video discs, record digital information streams as a series of pits and lands of selected length with the length of each pit defining a discrete digital value. Typically, optical discs are mass-produced by pressing a metallic master, having the digital information recorded thereon, into a plastic disc to impart the digital information onto the surface of the plastic. The master can be created in a number ways, for example, by spin-coating a glass disc-like substrate with a photoresist material (including, where necessary, a binder layer between the glass surface and the photoresist) and rotating the so-coated substrate while illuminating a selected lineal portion of a spiral track with a laser that exposes the photoresist. The laser is switched on and off in response to the digital data to be recorded with the laser beam repositioned radially along the spiral track. Thereafter, the photoresist is developed to remove unexposed material leaving only hardened photoresist. This photoresist preform is then subjected to one or more plating steps in which a metallic film (principally nickel) is formed on and overlays the photoresist pattern. The metal film is then removed and used as a master for pressing the plastic compact discs.
Various types of errors can be introduced into the recorded information, which errors can interfere with optimal recovery of the recorded information during the read operation. These errors can include, for example, errors in forming the start and the stop positions of the pits. These types of recording errors, known generally as jitter, constitute rapid short-term instabilities in the digital data stream that can compromise the quality of the output signal.
In the above described process, the amount of jitter encoded into the photoresist-covered glass disc cannot be directly measured. It is only after the first disc is pressed from the metal master that a jitter value can be ascertained. Once a jitter value has been determined, adjustments to the recording process can be made to make a subsequent photoresist-covered disc that presumably has a lower jitter characteristic. This process is repeated in an iterative manner until jitter is minimized to an acceptable level.
As can be appreciated, the above process is expensive from both a cost and time standpoint in that each iteration of the process requires formation and exposure of a photoresist-covered glass disc.